The present invention relates to a screening apparatus having a number of exchangeable screen elements, each of which has a screen surface with sieve-openings. The screen surfaces have a basic square or rectangular shape, and are placed onto intermediate cross-pieces along both their opposite and also longitudinal edges. The cross-pieces are attached to a carrier-framework.
The screening apparatus of this type is known from DE-A1-33-07-961. The attachment of the screen-grid or perforated bottom forming the sieve-surface to the intermediate cross-pieces is accomplished by means of profiled stops cooperating with the intermediate cross-pieces to hold the sieve screens or perforated bottoms. This structure involves two significant disadvantages. For one thing, sieve-lines form on the top-side of the entire screen-grid, due to the profile stops, which protrude upwards, since the profiled stops must naturally be located in the direction of forward motion of the sifting machine, and can not be covered by the sifting material as long as the thickness of the layer on the screen-surface does not exceed the height of the profiled stops which protrude upwards. Particularly with zonal application of sifting material, this prevents utilization of the entire breadth of the screen-grid. Moreover, active screen-surface is lost at the places where the sifting screen or the perforated bottom is held, which reduces capacity.